Transcript No Slide Title

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DNA  Deoxyribonucleic Acid
‘Deoxyribo’ refers to the sugar found in DNA
DNA is a nucleic acid- which is one of the
four major organic compounds we studied
earlier in the year.
Nucleic acids are composed of smaller
monomers put together called nucleotides.
DNA is often
called the
blueprint of life.
 In simple terms,
DNA contains the
instructions for
making proteins
within the cell.
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We study DNA for
many reasons, e.g.,
 its central
importance to all
life on Earth,
 medical benefits
such as cures for
diseases,
 better food crops.
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Our genes are on our
chromosomes.
Genes are instructions
to build proteins.
We all have the genes
but each of our genes
say different things.
That’s what makes
everyone unique!
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First isolated by Swiss scientists Friedrich
Miescher (1869) from pus from used
bandages.
The function of DNA was unknown but later
experiments proved that DNA was the genetic
material.
The next question to answer was to
determine the structure of DNA.
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James Watson and
Francis Crick solved
the mystery of DNA by
combining information
from Maurice Wilkins
and X-ray diffraction
from Rosalind Franklin.
Watson, Crick and
Wilkins earned the
noble prize in 1962.
Watson and Crick 1953
DNA is a very
long
polymer(many
nucleotides).
 The basic shape
is like a twisted
ladder or zipper.
 This is called a
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double helix.
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The DNA double
helix has two
strands twisted
together.
(In the rest of
this unit we will
look at the
structure of one
strand.)
The backbone
of the molecule
is alternating
phosphate and
deoxyribose, a
sugar, parts.
 The teeth are
nitrogenous
bases.
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phosphate
deoxyribose
bases
O
O -P O
O
O
O -P
O
One deoxyribose together
with its phosphate and base
O
make a nucleotide.
O
O -P O
O
Phosphate
Nitrogenous
base
O
C
C
C
O Deoxyribose
One strand of
DNA is a polymer
of nucleotides.
 One strand of
DNA has many
millions of
nucleotides.
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nucleotide
DNA has four different bases:
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Cytosine
Thymine
Adenine
Guanine
C
T
A
G
 Pyrimidines
are
single ring bases.
N C
O C
N
C
N C
 Purines
are
double ring
bases.
N
N C
C
C
N
N C
N C
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Thymine and cytosine each have one
ring of carbon and nitrogen atoms.
N
O
N
O
C
C C
N
N
C
C
thymine
O
C
C
C
N
C
cytosine
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and guanine each have two
rings of carbon and nitrogen
atoms.
Adenine
O
N
N
C
N
C
N
C
C
C
C
N
N
N
C
Adenine
N
C
N
C
Guanine
N
C
Remember,
DNA has two
strands that fit
together
something like
a zipper.
 The teeth are
the nitrogenous
bases but why
do they stick
together?
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N
N
C
N
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C
N
N
C
C
C
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The bases attract
each other because
of hydrogen bonds.
Hydrogen bonds
are weak but there
are millions and
millions of them in
a single molecule
of DNA.
(The bonds
between cytosine
and guanine are
shown here.)
O
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N
C
N
C
C
C
N
O
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When making
hydrogen bonds,
cytosine always
pairs up with
guanine,
And adenine always
pairs up with
thymine.
(Adenine and
thymine are shown
here.)
O
N
O
C
C
C C
N
C
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Adenine and Thymine always join
together
A
T
Cytosine and Guanine always join
together
C
G
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The bases form the “rungs” on the DNA
ladder by complementary pairing
A == T
C == G
T == A
G == C
A == T
T == A
Sugarphosphate
backbone
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Each cell has about 2
m of DNA.
The average human
has 75 trillion cells.
The average human
has enough DNA to go
from the earth to the
sun more than 400
times.
DNA has a diameter of
only 0.000000002 m.
The earth is 150 billion m
or 93 million miles from
the sun.
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In order for each cell to store all that DNA, it
must be packed into structures called
chromosomes.
DNA gets wrapped around protein like string
on a spool.
Those spools of DNA will continue to
condense to form chromosomes.